N-hydroxymaleamic acid



United States Patent 3,170,953 N-HYDROXYMALEAMIC AClD Sherman C. Lashua, Midland, Mich, assignor to The Dow Chemical Company, Midland, Mich, a corporation of Delaware No Drawing. Filed Sept. 6, 1960, Ser. No. 53,912 1 Claim. (Cl. 260-534) The present invention relates to hydroxamic acids, and is more particularly concerned with the novel compound, N-hydroxymaleamic acid, and its alkali metal salts. The invention also relates to a method of separating copper from solutions containing copper, cobalt and/or nickel ions.

1 have found that the reaction of hydroxylarnine with maleic anhydride, in a lower alkyl alcoholic solution, proceeds smoothly and rapidly to produce the new compounds N-hydroxyrnaleamic acid and its alkali metal salts in good yield and purity.

I have further found that N-hydroxymaleamic acid and its salts are capable of sequestering transition metal ions, particularly copper, nickel, cobalt and iron. In solutions containing copper, nickel and/or cobalt ions, copper is selectively precipitated at a pH in the range of about 2.5 to 5.0. The precipitation is essentially quantitative at a pH of about 4.0, thus afiording a clear separation of copper from nickel and/or cobalt.

The procedure which has been used for the reaction of maleic anhydride with hydroxylamine to produce N-hydroxymaleamic acid is shown graphically:

(enol form) Solutions of 69.5 grams (1 mole) of hydroxylamine hydrochloride in 325 ml. of methanol and 56.0 grams (1 mole) of potassium hydroxide in 140 ml. of methanol were prepared at reflux and then allowed to cool to about 40 C. The solutions were then slowly mixed with swirling and intermittent cooling in an ice bath. The resulting precipitate of KCl was removed by filtration and 98.0 grams (1 mole) of freshly crushed maleic anhydride was added to the hydroxylamine solution with stirring. The anhydride dissolved readily, and a white precipitate formed. After 3 hours the precipitate was collected, Washed with methylene chloride and dried in a desiccator. A yield of 60 percent of N-hydroxymaleamic acid was obtained having an initial melting point of 137 C. (enol form as established by nuclear magnetic resonance) which, on standing at room temperature, readily converts to the keto form melting at 125 C.

Analysis:

(keto form) Percent Percent Percent C H N Calculated 36. 7 Found 5 3,170,953 Patented Feb. 23, 1965 weights of 130 and 66.1 respectively. The theoretical values are 131 and 65.5.

The sodium and potassium salts of N-hydroxymaleamic acid were prepared as above except 2 moles of the appropriate alkali hydroxide were employed in the hydroxylamine neutralization, thereby providing a 1 mole excess for the subsequent reaction.

Yields of of the salts were obtained having the following analysis:

Sodium salt: Percent Na Calculated 15.0 Found 15.1

Potassium salt: Percent K Calculated 23.0 Found 20.0

N-hydroxymaleamic acid and its salts are exceptionally capable of sequestering iron over a pH range of 4 to 10. At a pH of 9 they are capable of holding approximately 0.5 pound of ferric ion per pound of reagent. Their ferric ion sequestering ability at 180 F. is greater than that of many other commonly used agents. Over the pH range of 5 to 9, about 0.60 to 1.5 millirnoles of ferric ion are sequestered per millimole of N-hydroxymaleamic acid.

The compounds of the present invention are useful for separating copper ions from nickel and/or cobalt ions in solution. In representative operations a solution containing 0.01 mole NiSO -6H O, 0.01 mole anhydrous CUSO and 0.02 mole of N-hydroxymaleamic in 100 ml. of Water was prepared. The initial pH was 1.9. Sodium hydroxide solution (1.0 N) was added slowly with stirring until the pH reached 3.9. After standing several hours at room temperature the precipitate was filtered, washed with water and dried. The following analysis indicates the removal of about weight percent of the copper from the solution.

Analysis:

Copper=25.0% Nickel: 0.05

A similar experiment using 0.01 mole of CoSO -7H O in place of the NiSO -6H O was performed with the following results, again representing the removal of about 95 weight percent of the copper from the solution.

Copper=25 .5 Cobalt: 0.03

Various modifications may be made in the present invention without departing from the spirit or scope thereof, and it is understood that I limit myself only as defined in the appended claims.

I claim:

A compound of the group consisting of N-hydroxymaleamic acid, and its alkali metal salts.

References Cited in the file of this patent UNITED STATES PATENTS 2,271,482 Hoelkeskam et al I an. 27, 1942 2,306,918 Weiss et al. Dec. 29, 1942 2,459,964 Robinson et al Jan. 25, 1949 2,859,243 Reed Nov. 4, 1958 2,970,036 Horton et al. Ian. 31, 1961 OTHER REFERENCES Ephraim: Inorganic Chemistry (edited by Thorne et -al.), 4th Ed., pages 652-653 (1947).

Fieser et al.: Organic Chemistry, 2nd Ed., pages 213- 216. 

